CVE-2023-5727: Windows Executable File Warning Bypass in Firefox and Thunderbird

A critical vulnerability has been discovered in the Mozilla Firefox and Mozilla Thunderbird software, allowing an attacker to bypass the standard executable file warning when downloading certain file types on Windows operating systems. The issue has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2023-5727 and affects Firefox versions up to 118, Firefox Extended Support Release (ESR) versions up to 115.3, and Thunderbird versions up to 115.4.

The Vulnerability

The security vulnerability lies in the way Firefox and Thunderbird handle certain file types that could potentially execute malicious commands on a user's computer. Specifically, when downloading files with the .msix, .msixbundle, .appx, and .appxbundle extensions, no warning is presented to the user, allowing for potential exploitation by a malicious actor without alerting the user. This issue only affects users running the affected software on Windows operating systems – other platforms are not impacted by this security flaw.

To illustrate the issue, let's consider an abbreviated code snippet from the affected application

if (isExecutableDownload(fileExtension)) {
    displayWarningDialog();
} else {
    proceedWithDownload();
}

The problem stems from the 'isExecutableDownload()' function, which does not account for the .msix, .msixbundle, .appx, and .appxbundle file extensions when checking for potentially executable file types.

Exploit Details

An attacker could exploit this vulnerability by tricking a user into downloading a malicious file with one of the specified extensions. The file would then bypass the standard executable file warning, potentially leading the unsuspecting user to run the malicious file on their computer. This could allow the attacker to gain unauthorized access to the user's system, steal sensitive information, or perform other malicious actions.

Thunderbird 115.4.1

Users of affected software versions are urged to update their installations as soon as possible to protect against potential exploitation of this vulnerability.

For more information, please refer to the original references

- Mozilla Security Advisory for Firefox
- Mozilla Security Advisory for Firefox ESR
- Mozilla Security Advisory for Thunderbird

Conclusion

This security vulnerability highlights the importance of thorough verification of file types and user warnings when handling downloadable files in desktop software. Fortunately, Mozilla has acted quickly to resolve the issue and released updated versions of the affected software. Users on Windows operating systems should update their Firefox and Thunderbird installations immediately to better protect themselves from this potential security risk.

Timeline

Published on: 10/25/2023 18:17:44 UTC
Last modified on: 11/02/2023 20:09:22 UTC